Ion gun



R. A. DANDL Oct. 24, 1961 'ION GUN 2 Sheets-Sheet I Filed March 29, 1960INVENTOR.

Raphael A. Dond/ ATTORNEY R. A. DANDL oct. 24, 1961 ION GUN 2Sheets-Sheet 2 Filed March 29. 1960 mumDOw ZO INVENTOR. Raphael A. Dand/mmnow 2@ ATTORNEY United i States Patent O 10N GUN Raphael A. Dandl, OakRidge, Tenn., assignor to the United States of America as represented bythe United States Atomic Energy Commission Filed Mar. 29, 1960, Ser. No.18,461 6 Claims. (Cl. 315-111) This invention relates to apparatus forthe production of an electrically neutral ionized plasma. Such a plasmamay be used in a variety of accelerators, mass spectrometers, hightemperattnechetniealreactors, and other electrical devices.

In conventional practice, a plasma is usually accompanied by anenergetic electron beam, and the plasma is commonly contaminated withvarying amounts, of neutral gas particles. Collision processes of theneutral gas particles and other attendant phenomenon seriously alter thebehavior of the plasma and :may render such a plasma uniit for varioususes. In conventional practice a plasma may be generated by electronbombardment of gas molecules as in an arc discharge such as disclosed inthe application of John S. Luce, Serial No. 833,897, iiled August 14,1959, now Patent No. 2,956,195, issued October 11, 1960. However, thedischarge of this application and other similar discharges are not freeof objectionable neutral gas particles. Still another characteristic ofthese prior discharges is that the voltage applied between widely spacedelectrodes to produce the discharges causes contaminants :from theelectrodes to be introduced into the .ICC

Y the annulus. The 'gas fed to the manifold is withdrawn therefrom intothe annulus between the anode and cathode by the pressure differentialthereacross and is substantially ionized by the arc discharge across theannulus. It has been determined that the plasmay produced by theapparatus of this invention will attain a reasonable density andstability when the immediate electrode is aligned with the annulus, 'forany given rate of -gas feed andmagnetic field strength. Theexistence'and positioningof the intermediate electrode isV a criticalfeature of the present invention. Little, if any, plasma is producedwhen this i electrode is o mitted. Furthermore, when this electrodeextends into the oteradia) portion 'of tire manner" TW rf-** that theannulus between the cathode and anode is not shadowed, the resultantplasma is small and extremely unstable. Thus, a satisfactory plasma canbe obtained only when the intermediate electrode is essentially alignedwith the annulus or is recessed into the inner portion of the manifold.The thus formed plasma is withdrawnfrom the annulus by thecombinedeffects of -thepressure differential and the magnetic iield.

The ion gun of this invention is considered suitable for providing aplasma toV be utilized in Va variety of devices characteristicallysimilar in that a plasma, i.e., an electrlcally neutral mixture of ionsand electrons, is employed therein for sundry purposes. Electricallyneutral plasmas are of interest in-the thermonuclear iields and forexperimental purposes; while charged ion beams, which may be produced bycharge separation and/or charged particle acceleration treatment ofneutral plasdischarges and also causes electric iields within thedismas, 'may be @56d ill Cllalged Particle aclel'als, maSS charges,particularly along the discharge, thus--resalting-inw.SQGCIGDJGCIS andthe llli-V certain instabilities therein. In addition, xuse Vof Widelyspaced electrodes in these prior discharges resulted in the necessityfor providing very special baiiles and differential pumping means toinsure stability of the discharges,

With a knowledge of the limitations of prior devices in the productionof a plasma, it is a primary object of this invention to provide an iongun for productionof a well defined, relatively uncontaminated plasma.

It is another object of this invention to provide an ion gun forproduction of a plasma that is characterized by very little extraneouselectrical fields, particularly longitudinal electric vfields along theplasma. y It is still another object of this invention to provide an iongun for production .of a plasma that requires no special balilesordiierential pumping means, and in which very little electrode materialis introduced into the plasma during operation of the ion gun.

These and other objects and advantages of this inven- 5 tion will becomeapparent upon consideration of the' following detailed speciiication andthe accompanying drawings wherein: y Y

FIG. 1 is a cross sectional view of a preferred embodiment ofthe-inventicnandsn- FIG. 2 is a cross sectional view of chine utilizingthe device of FIG. l.

The above objects have been accomplished in the present invention byproviding an evacuated system in which f there is contained an ion gunfor producing a plasma and a region where the plasma isto be utilized.The ion gun comprises an anode and a cathode mounted in concentricrelationship with a narrow annulus therebetween. The facing surfaces ofthe rear portions of the anode and cathode are recessed to form anannular manifold. Positioned within this manifold is an annularintermediate electrode aligned with the annulus between the anode andcathode. Gas is fed to the manifold and an arc discharge is establishedbetween the anode and cathode. A pressure differential is establishedalong theV annulus by the evacuated system anda uniform magnetic iieldis established so that the -eld lines traverse and are parallel to amirror type mau It is one aspect of this invention to utilize the iongun Y 1n a magnetic mirror type thermonuclear machine. When so used, theion gun is positioned at about center of one of the magnetic -mirrorregions` to assure as uniform a magnetic iield as possible in themanifold and annulus regions of the ion gun. The resultant hollow plasmawill follow the field lines and will terminate against some form ofbathe placed in or near theV second magnetic mirror region. This plasmamay then be used as a means for lthe breakup of molecular ions causingatomic ions to be formed and magneticallyl trapped within the Ihollowplasma, the plasma wall acting as a shield for the trapped atomic ionsagainst the instreaming of neutral particles from the iwalls of themachine, in a manner similar to that set forth in the application oflohn S. Luce, Serial No.- 833,897, iiledrAlugust 14,1959, entitled,Hollow Carbon Arc Discharge, now Patent No. 2,956,195, issued October11,Y 1960.

In FIG. l, one embodiment of the subject'device is shown. An anodeelectrode 1 and a cathode electrode 2 are mounted in concentricrelationship with a narrow annuluskS therebetween. The anode 1 ismounted on a conducting electrode support 4 which, in turn, is mountedsupported in one end wall of the housing 20. Cathode 2 is mounteddirectly uponv the end of a second support tube 6 which, in turn, isinsulatingly supported in the one end wall of housing 20.- 'I'he facingsurfaces of the rear portionsnof the anode and cathode are recessed toform an annular manifold 7. Positioned within this manifold 7 is anintermediate cylindrical electrode 8 which is mountedon a conductingelectrode support 9. This support 9, in turn, is mounted upon the end ofa third 'support tube 10. This tube 10 is insulatingly supported in theone end wall of housing 20. An exact spacing of this intermediateelectrode 8 with respect to the anode 1 and cathode 2 is accomplishedbythe insertion of an annular rinsulator 11 between support tube 10 andsupport tube ,5, andthe concentric annular insulator 12f between supporttube 6 and the electrode support 9, A vgas-tight `seal between thesecomponents is provided by the insertion of Q-rmgs or similar seals 13therebetween. The manner in which the electrodes are supported, asdiscussed above, 1s not lrnnted to the specific means set forth sinceany other conventional means may be employed fiar this purpose.

Electrode support 4 is provided with an axial passageway 1n whlch a tube14 is disposed. This passageway communicates with an axial passageway 15in anode 1. Passageway 15, in turn, communicates with radial passageways16 m anode 1. Feed gas, such as hydrogen or deuterlum, for example, isfed from a gas supply 21 through tube 14, passageways 15 and 16 into themanifold 7.

The housing 20 forms' a chamber 29 which is evacuated by means of avacuum pump, not shown, connected to a member 22 communicating with thechamber 29. Tube 6, which supports cathode 2,` is connected by anelectrical lead 28 to the negative terminal of a variable D.C. supply27. Tube 5, which is electrically connected -to anode 1, is connected bylead 24, switch 2 5, and lead y26 to the positive terminal of supply 27.Thenegative terminal of the supply 27 is grounded, as shown.

A uniform magnetic lield is provided by a concentric electromagneticcoil 2.3 disposed around the housing Coil 23 is energized by a source ofD.C. potential, not shown. The magnetic field lines provided by thiselectro.- magnet are in axial alignment -withthe annulus 3 b etween thecathode 2 and anode 1.

A baille 17 is disposed in confronting relation to the electrodes of theion gun and is mounted on the other end of housing 20 by an insulator18. Battle 17 may be grounded by a lead 19, and a switch 76, if desired.

Some of the dimensions and materials of construction of the device ofFIG. l are given below, by way of examples. The length of the anode andvcathode is 21/2 in.; diameter of anode is 11A in.; thickness of annulus3 is Af; in.; effective length of anode and cathode is l in.; outsidediameter of cathode is 2 in.; effective length of intermediate electrode8 is 1% in.; thickness of intermediate electrode is 1/15 in.; insidediameter of manifold 7 is 3:4; in.; and outside diameter of manifold 7is 1% in. The electrodes 1, 2 and 8 are machined from graphite stock,and the electrode supports and support tubes are copper. Steatite isused as the insulating material-for `members 11 and 12. The outsidediameter of the inter-- mediate electrode 8 is 1% in., so that the outersurface thereof is aligned with the inner surface of the annulus 3.

The above dimensions and materials of construction, with the exceptionof the position of the intermediate eltrode, are not critical to theoperation of the device of FIG. l. For example, the electrodes may beconstructed vfrom stainless steel, the insulating members may beconstructed from any of conventional inert insulating materials, and thedimensions of the electrodes and the annulus therebetween may be madelarger or smaller with substantially the same-operating results ifoperating parameters are modified accordingly. v

In a normal operation of the device of FIG. 1, the ion gun is aligned ina uniform magnetic eld, for example 3000 gauss, so that iield linestraverse and are parallel to, the annulus 3. The region external Vto theion gun in the chamber Z9 is evacuated to about 8 X10-5 mm. Hg or less.r[he pressure in the manifold 7 is at a higher value than in chamber 29during the time the device is producing a plasma. Gas is admitted to themanifold 7 vfrom gas supply 21 through passageways 14, 15, 16. With theintermediate electrode 8 electrically heating, a voltage is appliedbetween the anode 1 and cathode 2 by means of supply 27, and when thisvoltage reaches about 800 volts, a gas discharge is struck between theseelectrodes. The discharge can be initiated at lower voltages when themagnetic eld is higher. The voltage is then raised to an operating valueof about 1800 volts. The current flow between the anode and cathode isthen about 0.2 ampere for the spacing and pressure cited above.

Immediately upon striking the discharge, an ion plasma is formed alongthe magnetic field lines within and external to the ion gun. There is apressure differential across the annulus 3 by virtue of the differencein pressures between the manifold 7 and the chamber 29. The gas drawnthrough this annulus by this pressure differential is substantiallyionized by the arc discharge between the anode and cathode. The plasmathus emerging from the ion gun is relatively uncontaminated by neutralparticles. The plasma will follow the field lines until it strikes theelectrode or baille 17. The baie 17 may be used as a reflectingelectrode for the plasma which strikes it when the switch 76 is opened,or alternately it may be used as a collector electrode for the plasmawhen the switch 76 is closed. With a magnetic iield strength of 3000gauss and a voltage of 1800 volts between the anode and cath- Vode, aplasma of about 3 1011 particles/cc. is obtained. With a fixed rate ofgas feed and a fixed applied voltage, this plasma density has been shownto vary nearly proportionally to the square of the magnetic fieldstrength.

The` plasma of ions produced in the operation of the above-describeddevice doesnot haveany applied axial potential gradient therealong. Theabsence of such an applied potential gradient substantially eliminatesextraneous electrical iields, particularly longitudinal fields. Thus, itcan be seen that the plasma of ions produced by the device describedabove does not have certain of the objectionable electrical liieldswhich are characteristic of conventional gas-fed are discharges of theprior art. By positioning all the electrodes at one end of the device,less electrode material gets into the plasma as contaminant, and suchpositioning materially reduces baffling and differential pumpingproblems that are characteristic of prior art arc discharges.

It should be noted here that with the small current of .0.2 amperebetween the electrodes that there will be u minimum of electrode heatingand at this small current flow there with be less problem of theelectrodes disintegrating because of a lack of heat due to the smallcurrent flow between the electrodes. The device of this invention may beoperated at higher voltages and currents, and when so operated, coolingmeans for the elec-V trodes may be required. `When required, coolingcoils would be mounted on the -electrode supports.

It should -be noted here, in the event the plasma generator is used i-nan apparatus such as an accelerator or the like, that the housing 20 maybe eliminated and an evacuated region of such apparatus may provide thehereinbefore-mentioned means providing an evacuated system.

The principles of the ion gun discussed above may be used in a mirrortype machine such as disclosed in the embodiment of FIG. 2. A similartype of mirror machine is described in U. S. Patent No. 2,920,234,issued January 5, 1960, to John S. Luce, entitled, Device and Method forProducing a High Intensity Arc Discharge. In FIG. 2 of said patent theion gun is positionedin one of the magnetic mirror regions such that themagnetic Ifield lines traverse the annulus between the anode and cathodeand are substantially parallel with this annulus. The mirror machine ofFIG. 2 of the present application comprises an inner chamber 59 and twoend chambers 60 and 61. The inner chamber 59 is connected through anopening 63 to a .vacuum pump, not shown. The inner chamber 59 isenclosed by means of a liner 65. The liner .65 may be constructed fromstainless steel or Inconel, for example. The inner chamber 59 isenclosed with an outer enclosure 30. Enclosure 30 is provided with anopening 62 in communication with one of the end charnbers 60, and isprovided with an opening 64 in communication with the other end chamber61. Openings 62, 64 are connected to separate vacuum pumps, not shown,for evacuating chambers 60 and 6&1, respectively. Disposed in one end ofenclosure 30 is an ion gun assembly consisting of an anode 31, and acathode 32, defining an annulus 33 therebetween. Cathode -32 issupported by an annular tubular member 36. The anode 31 is supported bythe annular tubular member 35. Disposed within a manifold 37 between theanode and cathode is an intermediate electrode 3S. This electrode 38 isconnected to a concentric tubular member 4i). Disposed about the tubularmember 36 of the -ion gun assembly is an annular section of insulatingmaterial 73 which supports the concentric tubular members of the gunassembly and entends through the one end of the enclosure 3i).

Gas is supplied to the manifold 37 of the ion gun from a gas source 51,through a tube 44, and then through passageways in the anode 31. Themembers 35, 4t) and 36 are disposed in concentric relation with respectto each other and are held in a suitable spaced relation with respect toeach other by insulating means in the same manner as in the device ofFIG. 1. Member 36, which is electricdly connected to the cathode 32, isconnected to a source of D.C. supply v5'2" by a lead 5S. The other sideof DC. supply 57 is connected by a lead 56 to the member 35, which is inelectrical contact with the anode 31. rIlle D.C. supply 57 is a VariableD C. supply for supplying operating voltage between the cathode andanode. The anode, cathode, and intermediate electrode of the ion gun arepositioned in the center of a magnetic mirror region provided byA anannular electromagnetic' coil 66.

Disposed between coil 66 and the ion gun assembly are a plurality of bai67 disposed about the ion gun assembly. These baies 67 are insulatinglymounted on a portion of the inner chamber wall 65. A second annularVelectromagnetic mirror coil 66 is provided iat the other end `of thedevice and is mounted in concentric relation to a baflie or plate 47.This plate 47 is grounded through a plate support member 74, lead 49,and switch 75. The coils 66 and 66 are energized by a source of D.C.potential, not shown. The member 74 is encompassed or surrounded with aninsulating material 43 which extends through the other end of theenclosure 30. Disposed between the annular electromagnetic coil 66 andthe plate 47 are a plurality of annular baies 68. These baffles 68 areinsulatingly mounted on an extension of the inner' liner 65.

In the operation of the device of FIG. 2, the arc discharge isestablished in an identical manner to that described above for lFIG. l.After the arc discharge has been established between the anode 3i andcathode 32, the pressure diiferential across the annulus 33 between themanifold 37 and the innerachambcriris Such 35.10...

cause the gas within the manifold 37 to ow through the annulus 33 andthus through the arc discharge. The collimating effect of the magneticiield lines within the annulus 33 plus the pressuredifterential acrossthe annulus 33 will cause a plasma of relative uncontaminated ions to beejected from the ion gun in the form of a hollow beam 72. This beam 72will follow the magnetic iield lines provided by the mirror coils 66 and66', and any other coils that may be provided therebetween. 'This beam72 will follow the magnetic field lines until it strikes the plate 47.As in the device of FIG. 1, the magnetic iield strength is about 3000gaussfthe voltage aQIlQSSJhS e160- trode at operating value is about1800 volts, and a plasma of about 3X1()11 particles/cc. is obtainable.As in the device of FIG. 1, the plasma beam 72 of FIG. 2 issubstantially free of neutral gas particles because of the fact that thegas is substantially ionized by the arc discharge in the annulus 33before it leaves the ion gun.

This plasma beam 72 may be used as a dissociating mechanism in the samemanner as seti-forth in theaforementioned Patent No. 2,956,195. When theplasma as shown in FIG. 2 is used as a dissociating mechanism, a.Y

stream 71 of molecular ions yare injected from an ion source through anaccelerator 70 into the inside wall of the plasma 72 in an operatingzone between the mirror coils. A portion of the molecular ions 71, whenthey come in contact with the plasma beam 72, are dissociated by thisplasma beam into atomic ions and neutrals. 'The n atomic ions will bemagnetically trapped due to the effect of the coniining magnetic fieldand will form a ring of atomic ions. This trapping principle is -fullyset forth in the co-pending -application of John S. Luce, Serial No.728,754, tiled April 15, 1958. The portion of the rnc'-A lecular ionsthat are not dissociated by the plasma beam 72 will continue to move inthe same trajectory they had before contacting the beam 72. The neutralsformed in the dissociating process will ow off at a tangent to thepoints of dissociation and are lost to the system. These neutrals,however, may be used as an input to a particle accelerator, if desired.It should be noted that all electrical potentials for the device of FIG.2 are applied in.n

a zone removed from the operatingzone of the plasma between the mirrorcoils, thus preventing formation of ay longitudinal electrical iieldalong the plasma beam 72.' Absence of this field will insure betterstability of the plasma beam.

The plasma beam 72 of FIG. 2 is considered to be superior to the hollowcar on arc discharge of the aforementioned Patent No. 2,956,195, for thereason lthat the plasma 72 isessentially lfree of neutral gas particles,and therefore, when used as a dissociating mechanism, will not introduceextraneous matter or neutral particles into the plasma of atomic ionsformed in thetdissociating process. As discussed above for the device ofFIG. 1, the device of FIG. 2 will-produce -a plasma with Vlesscontaminants from'electrode materials than plasmas produced by prior arcdischarges. Also, there are less baffling and diiferentialV pumpingproblems withV the device of FIG. 2 than there are for prior arcdischarges. In addition, there are less electric fields produced in FIG.2 4than in prior arc discharges. As pointed out above, the plasma beam72 will serve as -a means for preventing the instreaming of neutralparticles from the walls of the machine, in a manner similar to that setforth in the aforementioned Patent No. 2,956,195.

The gas supplied to the ion gun of FIG. 2 may be hydrogen, for example,deuterium, tritium, or mixtures thereof. 'Ihe pressure in chamber 59 ismaintained `at a value of about 3 1O5.rnm. Hg, and the pressure in theend chambers and 61 is maintained at a value of about 1x10-4 mm. Hg, forexample. For some applications, lower pressures may be desirable.

The accelerator tube 7), referred to above, is energized by asuitable/high Voltage generator. The beam 71 of Wmolulanions mayihellqbor Dj, for egiample, 'andiale injected from the source 69 and throughthe accelerator 70 with an energy of about 600 kev.

Essentially all low energy neutral particles that strike the plasma beam72 are immediately ionized by the plasma and are pumped out of thesystem along the plasma beam and through the space between either thebaies 67 -and the ion gun or between the baffles 68 vand bafe 47 intothe end chambers.

The plasmas supplied by the ion gun of both FIG. 1 and FIG. 2 -aredierent from conventional yarc'discharges V in that they are relativelyquiescent and stable under their normal operationYconditimrfrnrventionatgas-are discharges may be and are usually highlycontaminated by neutral gas particles fed to the arc discharge. This isa disadvantage when they are used as dissociating mechanisms, for thereason that these neutral particles will interfere with the build up of,a suiciently dense plasma of atomic ions to the necessary density toprovide a ther- V monuclear plasma. It should thus be seen that theplasma beam of FIG. 2 is amore eiicient'dissociating mechv anism becauseof its characteristic of being relatively free from objectionableneutral gas particles and electrode contaminants therein.

This invention has been described by way of illustration rather thanlimitation, and it should be apparent that the invention is equallyapplicable in elds other than those described.

What is claimed is: I

l. An improved ion gun comprising a container, an ion gun assemblydisposed in one end of said container, said ion gun assembly comprisingan anode and -a cathode mounted in concentric relationship with a narrowannulus therebetween, an anode support member connected to said anodeand mounted in one end of said container, a cathode support membermounted to said cathode and disposed in said one end of said container,the rear portions of said anode and cathode being recessed to form anannular manifold, an intermediate electrode positioned within saidmanifold, a support member connected to said intermediate electrode andextending into said one end of said container, means for insulatinglysupporting said support members in concentric relation with respect toeach other, means for insulating said support members from said one endof said container, a source of gas supply, a gas supply feed tubeconnected to said gas source and extending through said membersupporting said anode, -an axial passageway within said anode conncctedto radial passageways within said anode, said radial passagewaycommunicating with said manifold, said gas feed tube being incommunication with the said axial passageway within said anode, a sourceof variable D.C. voltage, means for connecting said D.C. source betweensaid anodeV and said cathode, means connected to and in communicationwith said container for evacuating said container, a baille mounted tothe other end of said enclosure in confronting relation -with the `faceof said ion gun assembly, an electromagnetic coil disposed in concentricrelation around said enclosure, said electromagnetic coil supplying amagnetic iield, the magnetic ield lines of said coil being substantiallyparallel to and in alignment with the annulus between said cathode andsaid anode, said coil extending from an area adjacent to the electrodesof said ion gun assembly to an area encompassing said baie, saidintermediate electrode within said manifold being aligned with theannulus between said anode and Vsaid cathode, Ithe pressure within saidcontainer providing a pressure differential across said annulus, wherebythe larc discharge established between Said anodeand said cathode bysaid variable D.C. supply substantially ionizes `the gas owing throughsaid annulus by virtue of said pressure'differential to provide a plasmabeam substantially yfree of neutral gas particles.

Y 2. The ion gun set forth in claim l, wherein the magnetic eld strengthis about 3000 gauss, the region adjacent to the face of the electrodesof the ion gun is evacuated to about 8 l0r5 mm. Hg, the gas supplied tosaid manifold from said gas source is hydrogen, the voltage appliedbetween the anode and cathode is about 1800 volts, said intermediateelectrode being electrically oating, and the current ow between theanode and cathode being about 0.2 ampere, whereby said plasma beamprovided by said ion gun has a density of about 3 X 1011 particles/ cc.Y

3. An improved ion gun comprising a container, means connected to saidcontainer for evacuating said container, an ion gun assembly disposed inone end of said container, said ion gun assembly comprising an anode anda. concentricallydisposed cathode deiining an annulus between said anodeand said cathode, the rear portions of said anode and said cathodedefining a recessed manifold, an intermediate electrode positionedwithin said manifold and aligned with said annulus, a source of feedgas, means for feeding gas from said source into the interior of saidmanifold at a controlled rate, means connected to said anode, saidcathode, and said intermediate electrode for supporting them, saidsupporting means being mounted within one end of said container, Vmeansfor providing a containing magnetic field within said container toprovide magnetic eld lines that are parallel to and in alignment withthe annulus between said anode and said cathode, a source of variableD.C. supply, means for connecting said D.C. supply Vacross said anodeand said cathode to supply operating voltage thereto, the pressurewithin said container providing a pressure dif# ferential across saidannulus, whereby the arc discharge established across said anode andsaid cathode by said D.C. supply will substantially ionize the gassupplied to said annulus from said manifold, said gas being directed tosaid annulus by virtue of said pressure differential across saidannulus, said ion gun assembly thereby providing a substantially ionizedplasma which is collimated by said magnetic iield to supply asubstantially cylindrical hollow plasma to the evacuated region of saidcontainer.

4. The device set forth in claim 3 wherein the container is providedwith a central chamber and two end chambers, said ion gun assemblyelectrodes being positioned in one end of said central chamber, a bailledisposed in the other end of the central chamber, said magnetic eldbeing provided by a pair of electromagnetic mirror coils, one of saidmirror coils being disposed in concentric relation to the electrodes ofsaid ion gun assembly, the other mirror coil being disposed inconcentric relation to said baffle, said evacuating means beingconnected to each of said respective central chamber and said endchambers.

5. The device set forth in claim 4 wherein the central chamber isevacuated to a pressure of about 3 l05 mm. Hg, the voltage across saidanode and said cathode is about 1800 volts, the gas fed to the saidmanifoldis hydrogen, the magnetic iield strength supplied by saidmagnetic mirror coils is about 3000 gauss, said end chambers beingmaintained at a pressure of about 1x10-4 mm. Hg, whereby the plasmaejected from said ion gun assembly is substantially free from neutralgas particles, said plasma following the magnetic held lines provided bysaid mirror coils until said plasma contacts said baille.

6. The device set forth in claim 5 and further including a source ofmolecular ions, means for accelerating a beam of molecular ions fromsaid ion source into the inside wall region of said plasma at an anglesubstantially perpendicular to said plasma, said plasma partiallydissociating said beam of molecular ions into atomic ions, neutralparticles, and electrons, said atomic ions being magnetically trappedwithin the area defined by said plasma, and said neutrals being ejectedaway from said plasma.

References Cited in the tile of this patent UNITED STATES PATENTS LuceIan. 5, 1960 v corrected below.

UNITED 'sTL-Aii'lij"'P'T EN'ITOFFIQE CERTU?IGME 0F CORRECTION--- PatentNm1 3,005,931 i v october 24, 19er Raphael. A. Dandl It is herebycertified that error appears in the above numbered patent requiringcorrection and 'that the said Letters Patent should read as Column 7,line 56,l rfor '"xloll" made-e '3x1o-ll-- Signed and sealed this 15thday of May 1962e EAL) ttest:

ERNEST W. SWIDER DAVID L. LADD Y. Attesting Officer v ACommissioner ofPatent UNITED STTEPTENT@-oEEIEH i y CERTIFICATE 0F C@ERECTION-v`l` ,e

Patent No. 31,005,931 October 24; 1.961

RaphaellLA. Dandl It is hereby certified that error appears in the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below.

column 7, line 56 for "SXIVU" read-#-3XI01l-.-

Signed and sealed this 15th day of May 1962,

EAL) Hest:

ERNEST W. SWIDER DAVID L. LADD Y Attesting Officer e .Commissioner ofPatents

